Wisconsin’s Republican primary election on Tuesday might turn out to be Donald Trump’s “Waterloo.” Okay, that’s not a perfect example; a loss wouldn’t stop him in his tracks, but a defeat in the Badger State would probably stop him from clinching the Republican nomination.

There are many variables, but the simplified explanation goes like this: if Mr Trump loses Wisconsin and if Ted Cruz picks up a good share of delegates in California’s June 7 primary, then - assuming everyone wins the other states they are expected to win, based on past performances - Mr Trump will fall short of the 1,237 delegates needed to avoid a contested convention.

Watch | Trump calls Obama a 'baby' on the Iran nuclear deal

00:46

Now, on the surface, Wisconsin might seem tailor-made for Mr Trump. Unlike Texas and Ohio (the home states of Ted Cruz and John Kasich, respectively), none of his opponents hail from there. And unlike Utah, where he lost badly, Wisconsin is not a caucus, nor does it have a large percentage of Mormons.

Bethany Mead joins protestors against the businessman in Appleton, WisconsinCredit:
The Post-Crescent/AP

Moreover, Mr Trump tends to do well in “rust belt” states where plenty of non-college educated white voters (who do not happen to be Christian evangelicals) reside. What is more, Democrats and independents can vote in the Wisconsin primary, which tends to help Mr Trump.

But Mr Trump appears to be on the verge of getting trounced in the state. According to a recent Marquette University Law School poll (which is considered the gold standard in Wisconsin surveys), Mr Cruz has 40 per cent of the vote, Donald Trump has 30 per cent, and Ohio Gov. John Kasich is at 21 per cent.

There are multiple factors to explain this. Some of it is simply about Wisconsin’s unique political culture. You might have heard of “Minnesota Nice” or “North Dakota Nice.” Well, there’s also “Wisconsin Nice.” The state has what Wisconsin talk radio host Charlie Sykes described to me as a “Midwestern culture of civility and decorum” that simply does not jibe with Mr Trump’s in-your-face style.

Supporters of candidate Trump listen to his speech in the Wisconsin town of AppletonCredit:
Scott Olson/Getty Images

Mr. Trump suggested this week that a woman having an abortion should be punished - a position he quickly reversed after it became clear this angered pro-choices and pro-lifers, alike. Meanwhile, Mr Trump re-tweeted an unflattering picture of Heidi Cruz, the wife of Ted Cruz. That’s not "Wisconsin Nice".

“I’m under the impression that the way Trump behaves is more acceptable in the New York or New Jersey area,” said Mac Davis, a former state senator and retired judge, whose father Glenn Davis represented Wisconsin in the US House of Representatives.

Trump-ism also seems to thrive in places where there is a sense of social incohesion. But Wisconsin has high social capital - people there still join bowling leagues. It has become common for journalists to assume that Wisconsin voters ought to favour Mr Trump (based partly on his performance in states like Michigan), but it is important to remember that he came in a distant third in Minnesota’s March 1 caucus.

Another important factor explaining Mr Trump’s unpopularity is the uniqueness of Wisconsin’s influential local talk radio. Unlike some places that rely on syndicated content from national figures (most of whom, like Rush Limbaugh, have treated Mr Trump with kid gloves), Wisconsin boasts a thriving cadre of conservative talkers who haven’t been buying what Mr Trump is selling.

“Conservative radio here is not providing Donald Trump the air power he’s gotten elsewhere,” Mr Sykes told me.

The state, which is also home to Paul Ryan, Speaker of the House of Representatives, and Reince Preibus, the RNC Chairman, has a knack for producing serious conservatives.

Donald Trump turns away from the cameras as he speaks at a town hall event in AppletonCredit:
Mark Kauzlarich/Reuters

Lastly, Wisconsin Gov. Scott Walker has endorsed Ted Cruz (it is important to know that, in the span of four years, Mr Walker won three state-wide elections).

Mr Trump responded to Mr Walker’s endorsement of Mr Cruz by attacking the governor for (get this) not raising taxes (Mr Trump argued that this contributed to the deficit).

“The way Trump reacted to Walker’s endorsement, I just think is another solar flare of reaction by Trump that turns a lot of people off,” said Mr Davis.